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D M Landis

Publications and source records attributed to D M Landis.

66 records · Page 4Linked to original sources
PubMed1978

Internal organization of membranes at end bulbs of Held in the anteroventral cochlear nucleus.

The end of bulb of Held in the rostral ventral cochlear nucleus of the chinchilla and guinea pig was studied with the freeze-fracture technique. The end bulb has multiple, small active zones which are uniformly distributed within the calyceal portion of this terminal. Single or small groups of active zones are surrounded by enlarged channels of extracellular space often containing processes of astrocytes. Small plasmalemmal deformations occur at these active zones. The number of these deformations is thought to be indicative of exocytotic transmitter release because they are more frequent in animals fixed in a noisy environment compared to animals fixed in a quiet environment. Thus, our study provides a basis for the quantitative study of changes in transmitter secretion at a central nervous system synapse driven by a controllable natural stimulus. The postsynaptic active zone at end bulbs resembles other excitatory synapses in the central nervous system in having an aggregate of large particles on the external membrane leaflet. This junctional aggregate of particles is coextensive with the presynaptic active zone and with the postsynaptic density seen in thin sections. Several perisynaptic aggregates of particles are deployed around each active zone on the external membrane leaflet. These irregularly-shaped aggregates occur preferentially opposite the channels of enlarged extracellular space and along the edge of the end bulb and are not components of intercellular junctions or plasmalemmal contacts with cytoplasmic organelles. Although the function of the different particle aggregates on the postsynaptic membrane is not clear, our findings provide a basis for studying the factors controlling and maintaining their structure as well as more evidence that a consistent relationship exists between types of synaptic action and structure of the postsynaptic membrane.

Acoustic Stimulation↗
PubMed1978

Electron microscopic analysis of postnatal histogenesis in the cerebellar cortex of staggerer mutant mice.

Postnatal development of the cerebellar cortex has been compared in staggerer mutant and unaffected littermate mice. From postnatal day 3 to about day 21 the external granular layer in staggerer mice is decreased in thickness and area, and the number of postmitotic granule cell neurons is reduced. Those granule cells that are generated seem to differentiate normally, with the remarkable exception that they form only primitive junctions with Purkinje cell dendritic shafts. These specialized junctions are not superseded by the normal parallel fiber:Purkinje spine synapses and disappear by the third week. Purkinje cell somata and dendrites are smaller than normal at all stages examined. The dendrites are not confined to the sagittal plane as in the normal and, unique among mutant or other animals described to date, they exhibit virtually no branchlet spines. All other cortical synaptic relations of granule and Purkinje cells, including climbing fiber:Purkinje spine synapses, appear qualitatively normal. However, by 28 days virtually all staggerer granule cells have degenerated. While the primary genetic defect remains unknown, we postulate that the morphological abnormalities may be attributable to a block in the normal developmental relationship between granule cells and Purkinje cells. The small cell size and failure to form branchlet spines suggest that the Purkinje cell abnormality may be closer to the primary effect of the mutant gene than the more flagrant hypoplasia and degeneration of granule cell neurons.

Animals↗
PubMed1977

Structure of the Purkinje cell membrane in staggerer and weaver mutant mice.

The structure of the plasma membrane of Purkinje cell dendrites was examined in weaver and staggerer mutant mice. Purkinje spines in weaver mice have clusters of intramembrane particles which resemble those at normal synapses with parallel fibers, even though no parallel fibers are formed in this mutant. There are very few spines in the staggerer, and these manifest normal intramembrane structure at contacts with climbing fibers. The spines which would normally be involved in synapses with parallel fibers are never formed in the staggerer, and the intramembrane structures which would have been associated with these spine synapses are also lacking. Thus, during postnatal cerebellar development in the mutants, acquisition of intramembrane specializations requires Purkinje spine formation but can occur independently of the development of parallel fibers.

Animals↗
PubMed1976

Similarity of junctions between plasma membranes and endoplasmic reticulum in muscle and neurons.

The structure of membranes at junctions between the plasma membrane and underlying cisterns of endoplasmic reticulum in amphioxus muscle and mouse cerebellar neurons was studied using the freeze-fracture technique. In amphioxus muscle, subsurface cisterns of sarcoplasmic reticulum form junctions with the surface membrane at the level of the sarcomere I bands. On the protoplasmic leaflet of the sarcolemma overlying these junctions were aggregates of large particles. On the protoplasmic leaflet of the membranes of cerebellar basket, stellate and Purkinie cells there were similar aggregates of large particles. In both tissues, the corresponding external membrane halves had arrays of pits apparently complementary to the aggregates of large particles. Cross fractures through junctions showed that the particle aggregates in neuronal and muscle membranes were consistently located over intracellular cisterns closely applied to the plasma membrane. Thus, a similar plasma membrane specialization is found at subsurface cisterns in mammalian neurons and amphioxus muscle. This similarity supports the hypothesis that subsurface cisterns in neurons, like those in muscle, couple some intracellular activity to the electrical activity of the plasma membrane.

Animals↗
PubMed1975

Junctions in the meninges and marginal glia.

The meninges of various mammals were prepared for examination with the electronmicroscope by thin sectioning or freeze-fracturing. Particular attention was given to the distribution of tight junctions in order to determine the basis for the meningeal barrier between the blood circulating in dural vessels and the cerebrospinal fluid in the subarachnoid space. While some dural blood vessels are fenestrated, those in the subarachnoid space are not and their component endothelial cells are joined by an extensive system of tight junctions. An extensive and continuous system of tight junctions was also found in a layer of specialized cells at the border of the arachnoid with the dura. This arachnoid barrier layer is apparently the only basis of the meningeal barrier because often cellular layers in the dura and arachnoid lack tight junctions although they are linked by gap junctions and desmosomes. In particular, tight junctions are lacking at the border of the "subdural space" which is actually a fascial plane within the dura. Tight junctions are also lacking between astrocytes at the surface of the brain but these cells are linked by gap junctions and a new type of intercellular junction. The distribution of these junctions, as well as assemblies of intramembranous particles at the astrocytic border, raises the question whether this layer might have a role in the exchange of certain substances between the brain and cerebrospinal fluid.

Animals↗